Due to increasing levels of traffic pollution caused by vehicle exhaust emissions, new government legislations for lower exhaust emission limits, customer demands for lower fuel consumption and increased smoothness of the transmission there is a pressing need to improve the efficiency of engines and transmissions. Also in the field of motor sport the competition is very high and it is of utmost importance to apply the best technology for the race car engines and their drive trains.
Electronic control systems for combustion engines include a number of sensors and systems for determining various engine operating conditions. Many of these sensors are working in harsh environments and are subjected to widely varying operating conditions and the requirements on a sensor are very demanding in terms of durability, long term stability and the ability to operate over a large temperature range. Typical temperature ranges that are encountered in automotive applications range from −40° C. up to +150° C. In this temperature range it is required that the sensor produces a reliable output signal throughout its entire life.
One solution to the problem of temperature stability is to design a sensor that is sufficiently stable throughout the temperature range and throughout the lifetime of the sensor. The problem with such a sensor is that it is either too costly to produce for automotive purposes or too bulky to integrate in the power train.
Another solution is to add a temperature calibration step in the production where the temperature characteristics of the sensor are compensated by adjustments of the sensor or in the electronics. Since this operation has to be performed on each individual sensor in production this adds extra cost to the component.
A further complication is that a torque sensor for automotive applications is usually for practical reasons designed by two separate parts, where one part is the load carrying shaft and the other part is a surrounding yoke, which parts are combined first when the sensor is mounted on the gear box. A temperature calibration step of the offset drift of the sensor has to be performed on the complete sensor and can not be done on the separate parts. A further problem with the temperature calibration solution is that it does not account for long term effects on temperature characteristics.
A straightforward way to calibrate the sensor offset in the application is to perform a zero reset of the sensor during gearshifts, when the drive train is unloaded. A limitation of that approach is that the zero reset is only valid at that particular temperature level. When the temperature changes a new zero reset/calibration has to be performed in order to achieve reliable sensor data.
U.S. Pat. No. 6,658,345 describes how the temperature characteristics of a sensor can be compensated after installation in an application. A problem with this approach is that it requires the input of a separate temperature sensor. It further relies on a key switch for start and stop and can only update the sensor model at start or stop of the engine.